1. Field of the Invention
The present invention relates to an organic electroluminescent (EL) device for use in emissive displays, surface-emitting light sources, and the like.
2. Description of the Related Art
In recent years, organic EL devices have actively been developed. Thus, technologies regarding protective layers for blocking the intrusion of moisture and oxygen from the outside have also been studied to make full use of their luminescence properties. Protective layers need to not only block the intrusion of moisture and oxygen, but also have excellent optical properties from the viewpoint of luminescence.
Japanese Patent Laid-Open No. 11-242994 discloses a silicon nitride protective layer formed by plasma chemical vapor deposition (CVD) at room temperature.
In protective layers formed of silicon nitride, there is a trade-off between the optical properties and the protective performance. Specifically, the silicon nitride protective layer just formed by plasma CVD as described in the patent document exhibits higher light absorption, as well as high protective performance. Thus, although the silicon nitride protective layer has a small deterioration rate of optical properties in an endurance test, its initial optical properties are poor. Hence, the silicon nitride protective layer hardly makes full use of high luminous efficiencies of recent organic ELs.